The proposed study addresses the effect of unilateral right or left hemisphere lesions upon young children's language development, cognitive ability and academic achievement. The principal questions addressed include: Do the previously identified expressive syntactic deficits persist in left-lesioned subjects or diminish over time? Are difficulties in syntactic comprehension apparent as the children become older and more amenable to testing? Does the rate and nature of cues effect lexical retrieval differentially for left- and right-lesioned subjects. Are differences in cognitive profiles revealed at older ages on more discriminating measures? Are reading, writing and mathematic problems present at school age and are there differences between left- and right-lesioned children? And, can site of lesion within a hemisphere be related to the severity of deficit in a skill area? At the onset of this continuation study, 21 children with left lesions and 17 with right lesions have been recruited for participation in yearly testing. These unilaterally-lesioned children's performance on an extensive battery of language, cognitive and achievement measures will be compared to that of matched controls. The study addresses the issue of the limits of cerebral equipotentiality, provides data detailing children's language, cognitive and achievement abilities subsequent to left or right lesions, charts changes during development and relates lesion localization to resultant effect on higher cognitive functioning in children. Finally, the study provides information upon which clinicians can base their clinical judgments, treatment recommendations, remedial programs and prognostic statements for children with unilateral lesions.